Automatic switching system



Nav. 13,1945. BID. WILLIS 2,388,810

AUTOMATIC SWITCHING SYSTEM Original Filed Feb. 10, 1941 5 Sheets-Sheet 1 INVENTOR. BERNARD D. WILLIS, DECEASED v I W WALTER OWEN. EXEGUTOVV Nov. 13, 1945. I B. D. WILLIS AUTOMATIC SWITCHING SYSTEM Original Filed Feb. 10, 1941 3 Sheets$heet 2 4'.FlG.3

INVENTOR.

BERNARD D. WILLIS, DECEASED w WALTER OWEN. EXECUTOR ATTORNEYS Nov. 13, 1945. B. D. wu |s 2,

' AUTOMATIC SWITCHING SYSTEM I Original Filed Feb. 10, 1941 3 Sheets-Sheet 3 ago 1 RE 858 8 A l n N L 1% co INVENTOR.

'- N a BERNARD o. WILLIS, DECEASED BY wm. WALTER OWEN- EXECUTOR 8 ATTORNEY Patented Nov. 13, 1945 UNITED STATES 'ATENT orrics AUTOMATIC SWITCHING SYSTEM Original application February 10, 1941, Serial No.

Divided and this application October 15, 1942, Serial No. 462,089

6 Claims.

The present invention relates in general to automatic switching systems, and more in particular to such switching systems as include an impulse sender or calling device at a control station, a line extending to a distant switching station or exchange, and one or more automatic switches at the latter point which are selectively controlled over the line by the calling device at the control station.

An example of such a switching system is an automatic telephone system, in which each subscribers line is provided with a calling device at the subscribers telephone, and in which automatic switches are provided at the exchange for the purpose of establishing telephone connections under subscriber control. For convenience, therefore, the invention is illustrated and described herein as a simple form of automatic telephone system. It is not limited to such use,

however, but ma be employed in a variety of situations where it is desired to elfect selective action under remote control.

The main feature of the invention is the novel principle in accordance with which the selecting operation is controlled. In automatic telephone systems which are in common use, the control is exercised by the transmission of a variable series of impulses which are generated by a calling device. depends on the digit in accordance with which the calling device is operated, and the selecting operation resulting from the transmission of a series of impulses is in accordance with the number of impulses in the series. This principle of operation requires absolute accuracy in the registration of a, series of impulses and since the impulses must be transmitted at rather high speed, and frequently over lines ill adapted to high speed impulse transmission, certain difficulties have been encountered which render it more or less unsatisfactory.

In Patent No. 2,222,131, granted November 19, 194.0,, therev is described a system of selective control for use in automatic telephone systems or other automatic switching systems, which employs a single. impulse of variable length or duration, and in which the selecting operation performed in response to the calling of a digit is in. accordance with the length of the'single impulse generated b such. calling operation. A continuous. motion switch is used, which is started at the. beginning of the impulse and is stopped at the. end thereof. The-switch runs. at predetermined speed for the duration of the impulse, and the extent of its motion, or the selecting op The number of impulses in a series eration performed, is therefore in accordance with the length of theimpulse, In this system of control the duration of each impulse is determined by the digit called, but is also dependent upon the speed of the calling device, which accordingly must be coordinated with the speed of the automatic switches in order to insure accurate selection. The necessary speed relation between the calling device and switches is not particularly difficult of attainment, but this requirement nevertheless introduces a difficulty under certain circumstances, which renders the system less satisfactory than it otherwise would be,

The improved system of selective control resembles the system disclosed in the above mentioned patent to some extent; that is, it dispenses with the use of a variable series of impulses. At each operation of the calling device a fixed number of impulses are generated. Two impulses instead of one are generated, however, and although these two impulses areof variable length the selection efiected does not dependv directly upon the length of the impulses, but upon the ratio of the length of the first impulse to that of the second. Thus the speed'of the calling device, within reasonable limits, is entirel immaterial. For the digit 1, for example, the ratio of the duration of the first impulse to that of the second may be as 10 is to 1, A given calling device may operate at such a speed that the duration of the first impulse is one second, While the duration of the second impulse is one-tenth second. Another calling device may have a faster speed such that the duration of the first impulse is only one-half second, but the duration of the second impulse in this case will only be one-twentieth second, and the ratio between the two impulses will be the same.

It will be understood that the present improved system the calling device and likewise the switch under control thereof must run at some constant speed, but the two speeds do not have a fixed relation to each other and accordingly these requirements are easily met. For instance, the switch may be operated by a synchronous motor running on commercial power, which has a substantially constant frequency. The calling device, on the other hand, may be providedv with a speed governor, of which several reliable types are known. Since the calling device speed is. not rigidly associated with the switch speed, either speed may be varied within quite Wide limits without affecting the'selection control,

The practical application of the new principle mounted on the base i.

7. detail in connection with Fig. i.

, separated from contact spring 42.

.- This application is a division of the Willis application Serial No. 378,151 filed February 10,

1941, issued September 14, 1943, as Patent No. 2,329,234.

The foregoing and otherfeatures of the invention will be fully explained in the course of the following detailed description, reference being had to the accompanying drawings, in which- Fig. 1 is a front view of the calling device;

Figs. 2 and 3 are additional views of the calling device, Fig. 2 being a section on the line 2 -2, Fig. 3, and Fig. 3 being a section on the line 3--3, Fi 2;

Figs. 4 and 5 are fragmentary views showing details of the calling device;

Fig. 6 is a partial section on the line 6-6, Fig.

3, showing the commutator;

Fig. l is a diagrammatic circuit drawing of an automatic telephone system in accordance with the invention. The details of the switch mechanism are shown in said prior application.

Referring to Figs. 1 to 6, inclusive, the calling device will first be described. Fig. 1 shows the general appearance of the calling device when installed and ready for use. As seen in this figure, there is a base I, which may bea metal casting, and which is provided with rubber supports 3 at the corners. There is also a cover 2, of heavy sheet metalrand shaped as shown in Figs. 1 and 2. Itwill also be seen that a number of digit keys such as key 1, are, provided, which project through slots such as 8 in thecurved front of the cover 2.

There may be ten of these keys, numbered from 1 to 0, inclusive. At the left of the row of keys there is an escutcheon 5, which holds the directory card 6. At the right hand end the cover is completely closed, but at the left hand end there jisa circular opening (see Fig. 3), which is providedin order to afford access to the rear of the commutator 10 for wiringpurposes. This opening is closed by a detachable shallow cup-shaped closure member 4.

, ,Most of the parts of the calling device are To this end a U-shaped bracket. [0 is provided at one end of the calling ,device and an L-shaped bracket H at the other end. There is also an L-shaped bracket 46. These brackets may be fastened to the base i by means of screws, as indicated in Fig. 3. The shaft l2,is supported in bearings in the two brackets l0 and II and Supports the gear wheel, l3. The ten digit keys such as key 1 are also mounted on the shaft [2.

The arrangement of key 1 may be described in Reference may also be made to Fig. 2, which shows the key in loperatedposition. At the projecting extremity of the key there is a knob or ball 31, secured to the shank of the key by a screw 32. At the other lend the key is provided with. a hub 35, which is rotatable n the shaft 12. Projecting downwardly and to the right from the hub 36 there is an arm 39, provided for the purpose of controlling the contact spring 4], which is maintained normally A coil spring 40, better seen in Fig. 2, is attached to arm 39 and tends to rotate the key in aclockwise direction on shaft l2, thereby normally maintaining it in the position in which it appears in Fig. 4. The key 1 is also provided with a locking hook 33, the purpose of which will be described subsequently.

Associated with the key 1 there is a disk 3i, which is keyed or otherwise rigidly secured on shaft I2. The disk 31 has four notches spaced ninety degrees apart around its periphery, whereby it may be rotated by the key I through the medium of the pawl 3d, the latter being held against the disk by the spring 35. The slot 8 is long enough so that when the key T is operated (see Fig. 2), it moves through an arc of somewhat more than ninety degrees. Each time the key is operated, therefore, the pawl 34 engages in one of the notches 38 and rotates the disk 31 through an angular distance of ninety degrees. The rotation of the disk of course. rotates the shaft l2, since the disk is fixed to the shaft.

Each of the other keys is arranged the same as key I, and each of these other keys has associated with it a notched disk similar to the disk 31. When anykey is operated, therefore, the shaft 12 is rotated through an angular distance of ninety degrees.

The key locking mechanism will now be described. It comprises a shaft l4, rotatable in bearings in the brackets in and H, two arms 26 and28, which are rigidly secured to shaft 14 by keyed hubs 21 and 29, and a cross rod 30 which extends between the ends of arms 26 and 28 and is rigidly secured thereto. Associated with the arm 26 there is a coil spring 45, which tends to rotate the arm 26 and shaft M in a clockwise direction, such rotation being limited, however, by a stop screw 44 which prevents rotation of the arm 26 beyond the position in which it is shown in Figs. 2 and ,4. There may be a similar stop screw and spring associated with the arm 28, as indicated in Fig. 3. With this locking arrangement, it will be seen that when any key such as 1 is operated, its locking hook such as ,33 will depress the cross rod 30, rotating the shaft M through the medium of arms 26 and 23. When the hook passes the cross rod, the latter is raised again by the springs such as 45 and the keyis looked, as shown in Fig. 2.

The contact springs 4| and 42 associated with key 1 have already been referred'to. There is a similar set of contact springs associated with each of the other keys. springs are all mounted by suitable screws and insulators on a flat metal bar which may be formed integrally with the channel member iii. The latter extends lengthwise along the rear of the cover 2 on the outside thereof and forms a conduit for the conductors which lead from the sets of contact springs to the commutator 10. The channel member 5|, bar 50, and the sets of contact springs constitute a demountable unit which may be assembled and wired outside the calling device. When this unit is to be assembled in the calling device the bar and associated sets of contact springs are passed through an opening which is provided in the rear wall of the cover 2. This opening is closed by the channel jmember 5|, the cars such as 52 and 53 of which These sets of contact I closed positions of the set of contact springs 4=|-42 are shown in Figs. 4 and 2, respectively. I

Supported in bearings on the brackets l and there is a short shaft I8. The shaft 1 8 is adapted to be rotated by a pinion I5, which is in mesh with the gear wheel l3. The gear ratio is four to one, from which it follows that the pinion I and shaft H} are rotated three hundred and sixty degrees, or one complete rotation, each time a key such as key 'I is operated. This follows from the fact that the operation of a key rotates shaft 2 and gear wheel l3 ninety degrees and from the four to one ratio betwen gear wheel 13 and pinion l5. The gear wheel 43 is rotatable on shaft 18 and is connected thereto by means of a helical spring l6, one end of which is secured to the shaft H3 and the other end of which is secured to a pin This pin is rigidly fixed to the gear wheel 43 and projects from the side thereof, as shown in Fig, 3. The spring I6 is normally under tension, tending to rotate the gear wheel 43 in a clockwise direction, as seen in Fig. 2. Rotation of the gear wheel cannot normally take place, however, due to the fact that the pin I1 is held by the hook 51 on the end of arm 56, as shown in Fig. 4. The arm 56 is rigidly supported on shaft l4. Since the spring I6 is under tension, it also tends to rotate the shaft I8 and pinion 5 in a counterclockwise direction, but such rotation is prevented by the do 59 Fig. 2, which engages with the teeth of the gear wheel I3.

The gear wheel 43 is in engagement with a pinion 20, which is fixed on the shaft I9, the latter having bearings in the bracket l0. this shaft there is mounted the wind governor comprising vanes 2|. Any other known form of governor could be used here, such as a centrifugal governor, for example.

The commutator 10 may be of molded insulating material and has a row of contacts 6| to 60 and H embedded therein, as seen in Figs. 3 ands. There is also a ring 12 of conducting material. The commutator may be secured to the cover 2 by means of screws, as shown in Fig. 6.

The gear wheel 43 carries a pairof brushes 24 and which cooperate, respectively, with the contacts such as El and the ring 12. These brushes are supported in brush holders 22 and 23, which are insulated from the gear wheel, but are conductively connected together. The brush 24 is normally in engagement with contact II, and this contact is therefore normally connected through the two brushes to ring 12. When the gear 43 is rotated, the brush 24 leaves contact H and engages successively with contacts 60, 69, etc., which are thus connected successively to ring 72, since brush 25 maintains continuous contact with th rin The contacts such as H are each provided with a pin or stud such as 13, these pins extending through the commutator and projecting from the back thereof. There is also a pin 14 associated with the ring 12. These pins enable suitable cir-. cuit connections to be made to the commutator.

The wiring is shown in Fig. '7, where the calla ing device is shown diagrammatically and is indicated by the reference character CD. As shown, there are only two conductors leading in to the calling device, these conductors being indicated at 202 and 203. These conductors extend through a suitable opening in the closure member 4 (see Fig. 1),, to the rear of the commutator 10, where conductor 202 is connected to. the ring 12 by means of the pin 14. Conductor 203. is connected to contact H by means of its pin 13. This pin 13 is also connected to all of the contact springs such as 42 of the sets of contact springs which are associated with the keys. springs such as 4| of these sets of contact springs are wired individually to the pins such as 13 which are'associated with the commutator contacts 6| to 60. That is, contact spring 4| associated with the first key T corresponding to the digit 1 is wired to contact 6|, the contact spring corresponding to spring 4| but associated with the digit 2 key is wired to contact 62, and so on. There being ten keys, there will be ten conductors connected as described. These conductors, together with the additional conductor for connecting the contact springs such as 42 with the contact H, extend from the key contact springs by way of the conduit 5| and the extension 4' of the closure member 4 to the rear of the commutator, where they are connected as described.

Reference may now be made to the circuit drawing, Fig. 7, which shows the electrical connections of the system.

The-reference character A indicates a telephone, which may be of any suitable common battery-type. The conductors 200 and 28! extend from the telephone to a terminal strip 204, where the conductors 202 and 203 coming from the calling device CD are also terminated. At this terminal strip conductor 200 is connected directly to the line conductor 205, while conductor 2! is connected to the line conductor 205 by way of the calling device CD. In other words, the calling device is connected in series with one side of the line.

The line conductors 205 and 206 extend to' a switching station or exchange Where they terminate in an automatic switch indicated by the reference character S. This switch comprises a switch mechanism such as is shown in the above mentioned prior application, and. the control relays 2|0 and 2|6, inclusive. The functions of these relays will be explained shortly.

The switch S may have access to ten lines, one of which is shown, and comprises the line conductors 221 and'22'8. These conductors may extend to a telephone station B, which may be a common battery telephone simila to the telephone A. The relays 220 to 223, inclusive, are at the exchange and are individual to the line of station B.

A suitable source of current is provided for operating the switch, such as a storage battery, for example. In the circuit drawing connections to the negative pole of the battery are indicated by arrows accompanied by negative signs, while connections to the positive or grounded pole of the battery are indicated by the usual ground symbols.

The operation of the system will now be described, it being assumed for this purpose that a call is to be made from the station A to the station B. The line of station B is connected to the first set of bank contacts in the switch S and accordingly is selected by calling the digit 1.

When the receiver is removed at station A, a circuit is completed for the line relay 2| I, said circuit extending from ground by way of the lower winding of the line relay, contact 23L line conductor 206, conductor 20,3, contact 1|, brushes 24 and 25, ring 12, conductor 202, conductor 2M, telephone at station A, conductor 200, line conductor 205, contacts controlled at 230, and the upper winding of relay 2 to negative battery. Upon energizing, the line relay 2 closes a circuit for the slow-acting relay 2|2 at contact 232,

The other contact saidcircuit also including; contact 243. Upon energizing-in turn, relay 2I2- prepares certain circuits at contacts 234 and 235, and at contact 236' closes circuits for the brake magnets 116 and I11; These circuits include-the sets of -contact springs controlled by the armature I51 and will be apparent upon inspection; The brake magnets energize when their circuits are closed and their armatures grip the rollersshown in the above mentioned prior application to hold the switch from movement. I

The calling party at station A may now operate the calling device key corresponding. to the digit 1, rotating this key forward from its normal position as shown in Fig. 4 to the fully operated position ,inwhich it appears in Fig. 2. The operation of the key rotates the shaft -I2 through an angular distance of ninety degrees, and gear I3 and pinion I5 cause one full rotation of shaft I8, thereby winding spring I 6. As the key approaches its fully operated position the hook 33 depresses the locking bar 30, as shown in, Fig. 5, thereby rotating shaft I4 andarm 55 and moving the hook 51 far enough to the left so that it can no longer hold the pin. This operation releases the gear 43, which starts to rotate in a clockwise direction from power supplied by spring I6 and under the control of the governor 2I. When the key reaches its fully operated position, the shaft I4 is restored by spring 45 and the key becomes locked by bar 30, as shown in Fig. 2. The operation of the key permits contact spring M to engage contact spring 42, thereby connecting contact BI to the conductor 203.

When the gear 43 is released as described in the foregoing, it makes one complete rotation and then becomes locked in normal position, the operated key 1 beingreleased just before the gear wheel has fullyreturned to normal. The manner, in which these ,operations take place will be readily understood from the drawings, particularly Fig. 5. When the gear wheel approaches normal position and shortly before the pin I1 reaches its dotted lineposition, the said pin engages the cam surface 58 on arm 56, whereupon the further rotation of the gear wheel rotates shaft I4 and depresses the locking bar 30. This operation releases the operated key, which is restored to normal position by the spring 40. As soon as the pin I1 passes oifthe cam surface 58, the shaft I4 is restored instantly, the arm 56 is moved to the right, and the pin I1 passesinto the notch behind hock 51. The gear wheel 43 thus becomes locked again, as shown in Fig. 4. After the key has been released, reverse rotation of the shaft I2 and gear I3 is prevented by the dog 59. The slight retrograde movement that may occur before the dog engages a tooth of gear I3 does no harm because of the fact that the keys move through an are which is greater than ninety degrees.

, During the rotation of the gear wheel 43 the brushes 24 and 25 cooperate with the commutator contacts to transmit two impulses over the line to effect the desired control over the switch S, whereby the said switch is caused to select the line of station B. These so-called impulses are actually interruptions of the line circuit. When the brush 24 leaves contact 1| the line circuit is opened, starting the first impulse. As the brush 24' engages contact 50, 59, etc., the line circuit remains open, for these contacts correspond to the tenth, ninth, etc. digit keys, which are in normal position. When brush 24 reaches contact .6I, however, corresponding to thefirst digit key, the line circuit is'again closed, for contacts and 42 have been closed by theoperation of the key. The engagement .of brush 24 with contact 6| thus terminates the first impulse. The line circuit is again opened when the brush 24 leaves contact BI, which thus starts the second impulse.

.This impulse is terminated when the brush 24 bythe normal position contacts 1 I, leaving twelve spaces in which the line circuit may be interrupted when such-spaces are traversed by brush 2-4. Ten of these spaces are occupied by the contacts BI to 60, inclusive, there being a blank space on either side of the contact 1I. These spaces correspond to time-units, since the brush moves at constant speed. Thus it will be seen that during one complete rotation of the brush 24 the line circuit will be opened at contact H for a total period of twelve time units. The line circuit is not actually open for thiswhole period, however, for in the rotation of the brush it will pass over an active contact such as GI, thereby closing the line circuit for an interval of one time unit and dividing the total period of twelve time units into two complementary impulse periods, the sum of which is equal to eleven time units. In case the digit 1 is called, contact 6| is rendered active, and the first impulse comprises ten time units corresponding to the angular distance from contact II to contact 6| in a clockwise direction,whi1e the second impulse comprises one time unit, corresponding to the angular distance from contact BI to contact H in a clockwise direction. If the digit 5 is called, the contact is made active, the first impulse will be six time units in duration, and the second impulse will have a duration of five time units. The impulse ratio in this case is-six to five. The impulse ratios corresponding to the other digits willbe apparent from the foregoing and-are seen to range from ten to one (digit 1) .to one to ten (digit 0).

Proceeding now to a consideration of the operation of the switch S infresponse to the impulses, thefirstimpulse or interruption of theline circuit causes the line relay .2! I to deenergize and the circuit of relay 2I2 is broken. Since the latter relay is slow acting, however, it does not fall back immediately, .and a circuit is closed for the magnet I53, said circuit extending from ground by way of contact 243, contact 232, contact 234, contact 231, winding of relay 2I5, and winding of magnet I53 to negative battery. Relay 2I5 is energized over this circuit and prepares a circuit forthe change-over relay 2I3 at contact 242.

When the magnet I53 is energized, it operates the armature I51, thereby bringing a continuously rotating drive roller into engagement with a floating roller to move the wipers. At the same time the armature I51 separates the contacts I61 and IE8, thus deenergizing the brake magnet I11, and freeing the driven roller. The driven roller accordingl starts to rotate the drive shaft, winding a release spring, and the carriage II2 starts to move tothe right. As soon as the carriage has moved off normal the contact springs I and I86 are closed, thereby completing a locking .circuit forrelay 2 I 2. ,This relay accordingly remains energized throughout the first impulse, regardlessof its duration.

At the end of the first impulse the line circuit is closed and the line relay is again energized, breaking the circuit of relay 2| 5 and magnet I53. Relay 2I5 is slow acting and holds contact 242 closed long enough so that the line relay can close a circuit for relay 2 I3 at contact 233. Upon energizing, relay 2I3 locks itself at contact 238. The magnet I53 deenergizes when its circuit is broken, whereupon the armature I 51 is retracted and the drive roller is disengaged from the driven roller. 7 At the same time the contact springs I61 and I68 are allowed to close, thus again energizing the brake magnet I11. The brake magnet I11 now prevents reverse rotation of the drive shaft by the release spring. I

During the first impulse the carriage H2 is moved continuously to the right by the rotation of the shaft H6, and the pin I35 in the block I I8 travels along the slot I22 in the wiper arm I2I. The distance traversed, of course, depends on the speed of the switch drive, which should bear such a relation to the calling device speed that the pin I35 will travel the greater part of the length of the slot, the exact distance being immaterial within a considerable range. It may be assumed that when the first impulse is terminated the pin I35 has reached the point X; that is, it traverses the distance OX, the point 0 representing the initial position of pin I35.

When the second impulse is received the line relay 2 is again deenergized, and opens the circuit of relay 2I2, also the circuit of relay 2I3', but these relays remain energized over their locking circuits. The line relay also closes a circuit for the magnet I54, extending from ground by way of contact 243, contact 232, contact 234, contact 231, winding of relay 2 I4, and winding of magnet I54 to negative battery. Relay 2I4 energizes over the above circuit and at contacts 239, 246, and 2 4I disconnects the switch wipers I23, I24, and I25.

The magnet I54 is also energized, and operates armature I51, thereby causing the driveroller to engage another driven roller, and at the same time separating the contact springs I69 and I16. The brake magnet I16 is thus deener-gized and the rollers start to rotate the drive shaft. The drive shaft rotates another driven shaft by means of gears, thereby raising the block II8 and pin I35 and rotating the wiper arm I2I about its pivot. This pivot does not appear in the circuit drawing,

.Fig. 7, but is in alignment with the pin I35 when the latter is in normal position.

At the end of the second impulse the line relay again energizes, breaking the circuit of relay 2I4 and magnet I54. Upon deenergizing, relay 2I4 connects up the wipers I23, I24, and I25. When the magnet I54 deenergizes, the armature I51 is retracted, disengaging the drive roller from the driven roller and closing the contact springs I69 and I16. The rotation of the drive shafts is thus terminated and the shafts are held in their advanced positions against the tension of the release spring by the brake magnet I16, which enthen close, and the line conductors 265 and 266 are extended by way of contacts 246 and 241, wipers I24 and I25, bank contacts 254 and 255, and conductors 224 and 225 to the windings of the line relay 226. Relay 226 is accordingly energized over the calling line in parallel with the line relay 2II and closes a circuit for the ringing relay 223 at contact 266. Upon energizing, relay 223 connects a source of ringing current Gen. to the conductor 221 and 228 of the line extending to station B, said connection being made at contacts 263 and 264, and at contact 262 connects ground to the holding conductor 226. The grounding of conductor 226 operates relay 22I, which looks itself to ground at contact 266 of relay 226 and breaks the circuit of relay 223. The latter relay is slow acting and holds the ringing circuit closed for an interval after its circuit is broken. After relay 223 has deenergized this holding conductor 226 is maintained grounded by way of contact 266 of relay 226 and contact 26I of relay 22L n The grounding of the holding conductor 226 completesa circuit for relay 2I6, extending from ground on said conductor by way of bank contact 253, wiper I23, contacts 239, and winding of relay 2I6 to negative battery. Upon energizing, relay 2I6 disconnects the line relay 2 from line conductors 265 and 266 at contacts controlled at 236 and at contact 23I, and at contact 236; closes a local circuit for the line relay including the resistance 245. held energized.

When the call is answered at station B, the calling and called parties may carry on a conversation in known manner. Current for the transmitter at station B is supplied through the windings of the impedance coil 222, while current for the transmitter at station A is supplied through the windings of the line relay 226.

The release of the connection is brought about by the replacement of the receiver at the calling station A. When the receiver is replaced, the line circuit is interrupted and the line relay 226 is deenergized, opening the circuit of relay 22I and removing ground from the holding conductor 226. Relay 2I6 accordingly deenergizes and breaks the circuit of the line relay 2I I. Upon deenergizing, the line relay closes the previously described circuit including relay 2I4 and magnet I54, the said relay energizing and disconnecting the switch wipers as before. Magnet I54, upon energizing, brings drive and driven rollers into engagement and also opens contact springs I69 and I16 to deenergize the brake magnet I16; Rotation of the drive shafts now ensues, which raises the blo'ck H8 and pin I35 in the manner previously described. Themovement of the block and pin continues until the latter engages the rod I38, whereupon a circuit is closed for relay 2I6, extending from the grounded frame of the switch by way of pin I35, rod I38, and winding of relay 2I6 to battery. Up'on energizing, relay 2I6 locks itself at contact 244, and at contact 243 it breaks the circuit of relay 2I4' and magnet I54 and also the circuits of the brake magnets I16 and I11. The deenergizati on of magnet I54 disengage's the drive roller from" the driven roller and stops further upward movement of the block H8. The

The line relay 2 isthus 6 deenergiz ation of the brake magnets leaves the drive shafts free, with the result that they are rotated in the reverse direction by the release springs. Thus the block H8 is lowered until it again rests on top of the carriage H2, while the ing circuits of relays 2I2, 2I3, and ZIB. These relays therefore deenergize and the switch is com- I pletely restored to normal, ready for another call.

The manner in which the switch is operated in response to the calling of other digits will be readily understood. When the digit 7 is called, for instance, by operation of the digit key corresponding to the digit 7, the calling device CD transmits two impulses having an impulse ratio of four to seven. In response to the first of these impulses the carriage II2 moves to the right during an interval of four time units and the pin I35 reaches the point X. In response to the second impulse the block II8 moves vertically during an interval of seven time units and carries the pin I35 to the point Y. The wiper arm is rotated during the movement of block H8 and takes up a position along the line O-.-Y, thereby positioning the wipers on the seventh set of bank contacts. The

other digits are called in the same way. It may be stated generally that the impulse ratio is difierent for each digit and that when any digit is called the pin I of the switch is moved along the two sides of a right triangle in which the lengths of the sides bear the same ratio to each other as the impulse ratio. The wiper arm is in any casepositioned along the hypotenuse of the triangle, a line the slope of which is determined by the relative lengths of the sides and not by their absolute lengths.

It will be easily seen now why the speed of the calling device can be varied independent of the switch drive speed without afiecting the accuracy of selection. Suppose, for example, that the calling device speed increases, which will decrease the length of the impulses, although maintaining the same ratio between them. It may be assumed that the increase in speed is so great. that when the digit 7 is called the length ofthefirst impulse is only sufiicient to advance the pin I35 to the point X" insteadof to the point X. The second impulse is correspondingly shortened, however, so that in its vertical movement the pin I35 is raised only to the point Y. The point Y5 lies on the line O- Y', from which it will be seen that the final position of the wiper arm isthe same regardless .of the change in the speed of the calling device.

It, will be appreciated that,.while'a comparatively simple telephone system has been shown herein, the principle of selection disclosed may be used in larger systems, followingknown methods employed in expanding the capacity of automatic telephone systems in common use. It will be understood also that this new principle of selection ,may be employed to advantage in various other automatic switching or indicating systems, and in such cases thenumber of selections or the number of calling device keys may be increased beyond the number shown herein. Nor is the invention ,limited to the precise impulse ratios explained herein, which have been selected merely as acon- -venient illustration of the principle involved,

Various other modifications may be made withassume inthe 'spirit'of the invention, and, it is not there 3 fore wished to be restricted toithe ejiact former the invention which is shown and described-hors in, but it is desired ,to'i emde ah dhavc rotected by Letters Patent all' forms'and modifications of the invention which come within'the' scope of the appended claims. I 5

-What is claimed is: v 1. In a calling device for sendingjsignals corresponding to digits, a plurality of operating meme bers, two circuitelements normally connected together, means responsive to the actuation gra one of said members to send a signal for automatically twice disconnecting said elements in any signal, and means for predetermining the relative lengths of said disconnections in accordance with the member actuated. T 2. A calling device for variably influencing a control circuit to transmit signalsthereoverfrepresenting digits, comprising a series of keys, arotating element, means controlled by the operation of any key to rotate said element always the same amount to open the control circuit for a certain time, and means controlled by the particular key operated to divide said time into: two different times by momentarily afiecting the circuit in another-way only once, the ratio of one open circuit timefto the other varying with the key operated. I V

3. A' calling device for use in automatic'telephone systems, having means for transmitting only a pair of impulses over a line circuit to represent any digit in response to each' operation of the device by opening said line circuit, means in the device for varying the length of one impulse caused by opening said line circuit relative to the length of the other, the ratio of one impulse to the other varying in accordance with the digit which the particular pair of impulses represent.

4. In a calling device for use in an automatic telephone system, a plurality of control members,

means responsive to the operation of each control member for operating the device to open a line circuit at one point in the operation and close the'same atanother point, and means for momentarily closing said circuit at only one point between said first two points, the-point at which the circuit is closed dependent upon the control member used to operate the device, whereby said line circuit is opened for two time intervals having difierent ratios dependent on the control member used to operate the device. 1 r 1 5. In an impulse sender for sending signals'corresponding to digits, acontrol circuit, means controlled by each operation of said sender, to-transmit a digit, for opening said control circuit for a predetermined length of time, and means for mo -mentarily closing said circuit once during each operation at a point to divide said open circuit time into two different complementary periods,

the ratios of the time of one open circuit periodto the time of the other determining the digit transmitted. W 6. In an impulse transmitter for sending signals corresponding to digits; a closed control circuit, means for causing two breaks in said control circuit to transmit each of the digits, said brakes being of differentduration' for. each digit-and means in the transmitter for predetermining the ratio of the time of one break to the time of the other before the transmitter is operated to send WM, WALTER ow-EN. Executor of the Estate of Bernard D. WiZlisIiie- .cw r y" 1 1 

